The present invention refers to an apparatus for carrying out wet chemical reactions under pressure comprising a pressure vessel in which a reaction liquid can be provided and which is adapted to be sealed in a pressure-tight manner by closure means.
Such apparatuses for carrying out wet chemical reactions under pressure are known e.g. from U.S. Pat. No. 4,882,128 or from European patent applications EP 0 416 759 A1 and EP 0 461 383 A2.
Wet chemical reactions, such as disintegration and decomposition, hydrolysis or synthesis, are very important for analysing and synthesizing substanes. The higher the reaction temperature is, the faster and the more complete such wet chemical reactions will normally take place. Hence, closed reaction vessels are used in accordance with the above-mentioned prior art so that higher pressures and, consequently, higher boiling temperatures of the reaction liquid for the wet chemical reaction can be used. For this purpose, the reaction liquid is provided in a pressure vessel whose interior can be acted upon by pressure. When the reaction mixture is heated, e.g. by a microwave field generated by a microwave generator, the desired increase in the reaction speed is achieved, whereby new possibilities are provided for efficient methods that can be used in the analysis and synthesis of substances.
Closed reaction vessels have, however, various drawbacks. The pressure in the vessel results from the sum of the partial pressures of the substances contained in the pressure vessel. The total pressure is therefore composed of the vapour pressure of the reaction liquid and of the partial pressures of the gaseous reaction products. In view of the limited mechanical stressability of the closed pressure vessel, the sum of the partial pressures must not exceed a specific maximum pressure. It follows that, the higher the partial pressures of the gaseous reaction products formed in the course of the reaction, the lower the maximum applicable vapour pressure of the reaction liquid will be. This means that, in view of the fact that the vapour pressure increases continuously as the temperature increases, there is an upper limit to the temperature of the reaction liquid.
In the case of oxidative acid decomposition of organic samples, for example, gaseous carbon dioxide is produced. The larger the amount of organic substance that is decomposed in a specific pressure vessel at a constant pressure is, the lower the vapour pressure of the decomposing acid must be and therefore the lower the maximum possible boiling temperature will be.
A further drawback occurring when closed reaction vessels are used is to be seen in the fact that the gaseous reaction products cannot escape and that, consequently, the reaction equilibrium is displaced towards the starting product.
Taking into account the drawbacks of the prior art, it is therefore the object of the present invention to provide an apparatus for carrying out wet chemical reactions under pressure of the kind referred to at the beginning by means of which a faster and more efficient course of reaction can be achieved.
According to the present invention, this object is achieved by an apparatus of the type referred to at the beginning, which is characterized in that a rinsing device is provided for rinsing the pressure vessel while removing gaseous reaction products from the pressurized pressure vessel and while maintaining a predetermined pressure therein. The present invention therefore permits wet chemical reactions to be carried out under pressure while continuously removing gaseous reaction products, whereby an influence of the partial pressures of the gaseous reaction products on the total pressure in the interior of the pressure vessel is excluded. In addition, the displacement of the reaction equilibrium towards the starting products, which increasingly inhibits the progress of reaction, is prevented by the continuous removal of the gaseous reaction products from the. pressure vessel acted upon by pressure.
According to an advantageous further development, the rinsing device comprises a source for a pressurized gas as well as a first gas conduit extending from said source into the interior of the pressure vessel, and, in addition, a second gas conduit extending from the interior of said pressure vessel to the outside thereof and including a first restrictor for producing a first predetermined flow rate. Preferably, also the first gas conduit includes a restrictor for producing a predetermined flow rate. Said first and second gas conduits including said first and second restrictors constitute a simple, but efficient embodiment of the rinsing device; by means of the restrictors in said first and second gas conduits, the flow rates for the supply and discharge of a purge gas can be preselected such that a pressure, which is predetermined by means of a pressure regulator valve, can be maintained in the reaction vessel. This predetermined pressure determines the boiling temperature of the reaction liquid.
According to a further advantageous embodiment, said first and second restrictors each comprise means for adjusting a flow rate. It follows that the conditions for carrying out wet chemical reactions can be adjusted individually, e.g. in dependence upon the reaction starting and end products.
According to a further advantageous embodiment, the apparatus for carrying out wet chemical reactions under pressure comprises a recondensation device provided in the interior of the pressure vessel and used for condensing evaporated reaction liquid. This recondensation device prevents losses of reagents and of important constituents of the sample. Hence, the efficiency of the wet chemical reaction under pressure is increased still further.
In accordance with advantageous further developments, this recondensation device can be implemented either as a cooling body which is adapted to be cooled such that the evaporated reaction liquid condenses, or as a means for applying a cooling gas stream to an area of the reaction vessel constituting an upper area with regard to the direction of the force of gravity, said reaction vessel being arranged in the pressure vessel and being adapted to hold the reaction liquid in a lower area thereof.
In accordance with a further advantageous development of the present invention, a heating device is provided for increasing the temperature of the reaction liquid. In accordance with an advantageous embodiment, this heating device consists especially of a microwave generator for generating a microwave field passing through the reaction liquid. By means of the microwave field produced by said microwave generator, a predetermined temperature-time characteristic can be controlled precisely through the power of the microwave field. In the case of a predetermined constant microwave power, a freely selectable time-temperature characteristic of the reaction liquid can also be achieved by controlling the pressure in the interior of the pressure vessel by the pressurized purge gas supplied, provided that a controllable pressure regulator valve is used in the gas conduit leading into the pressure vessel.
According to a further advantageous embodiment, a device is provided for feeding gaseous or liquid reaction substances into the pressure vessel. This feed device preferably comprises a multiway valve with a sample loop, said multiway valve being adapted to be switched at least to a first and to a second position for receiving in said sample loop a substance to be fed under a preselectable pressure at said first position and for feeding the received substance into the pressurized pressure vessel at said second position. With the aid of the multiway valve, a substance to be fed can be introduced e.g. without pressure into the sample loop of the multiway valve so that the amount of the substance to be fed can be determined precisely. When the multiway valve is switched to the second position, the substance introduced into the sample loop is fed under pressure into the pressure vessel.
According a further advantageous embodiment, a temperature sensor is provided for determining the temperature of the reaction liquid. This temperature sensor is especially arranged in a channellike indentation provided in the area of the lower end of a reaction vessel, whereby a particularly precise temperature measurement is possible.
Further advantageous embodiments are disclosed by the subclaims.